Nokia Certification 4A0-265 Reddit Questions

A “Loss of Signal” (LOS) alarm is a critical alarm that indicates that there is no or very bad signal at the physical interface. LOS alarm is also raised when the signal level drops below the threshold, at which a high bit error rate (BER) is predicted. LOS alarm can be caused by physical damage, power outage, or misconfiguration of the equipment. LOS alarm can affect the service availability and performance of the optical network. Therefore, it is typically assigned a critical severity level, which means that it requires immediate attention and resolution2. Other severity levels are major, minor, and warning, which indicate different degrees of impact and urgency of the alarms. References: Troubleshooting Guide for Cisco NCS 1002, T1: A Survival Guide, M-series SONET/SDH alarms and troubleshooting tips

The statement that best describes the Forward Error Correction (FEC) technique is C. FEC is a technique used in digital communication to improve the accuracy and reliability of data transmission. By adding redundant information to the transmitted data, FEC enables the receiver to detect and correct errors without retransmission or other error correction techniques11. FEC is effective only above a specified OSNR threshold, which is the minimum optical signal-to-noise ratio required for error-free transmission with FEC enabled. If the OSNR falls below this threshold, FEC cannot correct all errors and data quality degrades significantly. References : Nokia Optical Diagnostics and Troubleshooting Course | Nokia, Optical User Guide - Nokia, Forward Error Correction (FEC) - Online Tutorials Library

The exhibit shows a diagram of a network of nodes and edges, where a single directional fiber cut is occurring between two amplifiers in bidirectional configuration. The node that will report a “LD Input LOS” alarm is node B only. A “LD Input LOS” alarm indicates that the input signal to the laser diode (LD) of an amplifier is lost or below the threshold3. In this case, node B will not receive any signal from node A due to the fiber cut, and will generate this alarm. Node A will not report this alarm, because it can still receive a signal from node C through the other fiber. Node C will not report this alarm either, because it is not directly affected by the fiber cut between node A and node B. References : Nokia Optical Diagnostics and Troubleshooting Course | Nokia, Troubleshooting Guide for Synchronous Digital Hierarchy - Cisco

The command show wavekey wtmonitor 1/6/LINE summary displays a list of all channels detected against the selected interface (in and out); it shows if a Wave Keys pair is expected, if a Wave Keys pair is received, and if the received Wave Keys pair is unexpected. A Wave Keys pair is a pair of unique identifiers that are transmitted along with an optical channel to provide channel identification and monitoring functions. The command can be used to verify the presence and correctness of the Wave Keys pairs on an interface and to detect any mismatch or misconfiguration. The other options are incorrect because they either describe a different command or provide incorrect information. References: Nokia Optical Diagnostics and Troubleshooting Course, OAM and Diagnostics Guide